Terrestrial satellite transmitter systems are used to uplink signal transmissions in satellite communications networks. Typically, a satellite transmitter system includes a power amplifier to increase the power of the signal to levels adequate to reach a distant satellite with sufficient strength. Because the output power of a single amplifying element is often not strong enough, the outputs of many amplifying elements must be combined. Additionally, as the frequency of the transmitted signal becomes higher, the cross-section of the waveguides used to convey the signals must become smaller. As a result, different methods of power combining must be employed, often using one or more printed circuit boards (PCB) to manage these higher frequency wave signals. For example, conventional waveguide designers have employed many different techniques to combine the power of a higher frequency wave signal, such as using finline antennas, slotline antennas, or waveguide probes and transitions, often launching the waves into oversized waveguides. Generally these combiners propagate the amplified wave into a waveguide and eventually radiated to a desired satellite.
For instance, one conventional power combining technique includes using solid state amplifiers with tapered finline antennas printed on a single dielectric substrate (i.e., PCB) card in the center of an oversized waveguide. Despite the use of multiple finline antennas on a single substrate card to facilitate power combining, this conventional single substrate card technique limits the scale of power combining because only a finite number of finline antennas may be printed on a single substrate card. Moreover, because an oversized waveguide is often utilized in this single card technique, the possibility of spurious resonances increases because overmoding is more likely to occur (i.e., more than one mode propagation may occur at higher frequencies). Furthermore, this technique often directly connects each amplifier to adjacent amplifiers. This direct DC couple between amplifiers increases the possibility of low frequency oscillation problems in addition to other stability problems.
Another conventional technique utilizes multiple dielectric substrate cards that include tapered slotline or probe-like antennas that only have a single-end (i.e., only one single arm of the probe antenna) coupled to a single amplifier in conjunction with an oversized waveguide. Detrimentally, this conventional single-ended configuration often requires the use of a balanced-to-unbalanced (i.e., balun) transformer or other structure to assist with converting between a balanced signal and an unbalanced signal. As a result of incorporating a balun structure in the configuration, the bandwidth may be limited and undesired reactance may be introduced into the system leading to less favorable signal quality. Moreover, a single-ended configuration cannot sufficiently suppress harmonic interference as well a differential configuration, and again, overmoding issues are prevalent for applications utilizing oversized waveguides.
Other conventional power combining techniques include using a spatial waveguide power combiner that includes multiple trays of tapered slotline antennas, with wirebond transitions from the antenna to a microstrip on a dielectric PCB card. Not only do wirebond transitions complicate the manufacturing process, but they reduce the possible bandwidth usage of the wave signal. Moreover, because this configuration requires a more gradual taper in the slotline antenna to achieve a sufficient impedance matching over a substantial bandwidth, the entire slotline module that amplifies the power must be physically longer in length which adds weight and bulk to the power amplifying module.
Yet another conventional power combining technique includes implementing a tapered slotline-to-microstrip structure in which the differentially driven microstrips couple to an amplifier for eventually combining power into an output wave signal. However, this conventional technique suffers similar problems as other conventional techniques such as requiring an increased length of the device because, as described above, the gradual tapering of the slotline helps the system to achieve sufficient matching. Furthermore, despite the amplifiers being differentially driven, the amplifiers are coupled at DC with other adjacent amplifiers which may lead to low frequency oscillations and stability problems.